The present invention relates to a technique for providing an engine piston pin with low-friction characteristics and durability.
Global environmental problems, such as global warming and ozone layer destruction, are coming to the fore. The global warming is significantly effected by CO2 emission, and the reduction of CO2 emission (notably, the setting of CO2 emission standards) has become a big concern to each country.
Herein, one of the challenges to CO2 emission control is to improve vehicle fuel efficiency. The sliding friction of piston pins against piston pin bosses in a vehicle engine is largely responsible for engine mechanical losses. It is thus important to reduce the friction between the piston pins and pin bosses in order to provide a direct improvement in vehicle fuel efficiency.
There are effective ways to reduce the friction between the piston pins and pin bosses: one way is to protect the piston pins from seizing, and another way is to save the weight of the piston pins while preventing the piston pins from wear. For example, Japanese Laid-Open Patent Publication No. 7-286696 proposes covering the piston pins with high-hardness metal coatings so that the so that the piston pins become more resistant to seizure. Further, Japanese Laid-Open Patent Publication No. 8-061499 proposes forming the piston pins from a ceramic material so that the piston pins become lightweight and resistant to wear.